The present invention relates to a pneumatic tire, more specifically, a pneumatic tire in which air permeability is significantly decreased.
A tubeless tire wherein an air chamber is formed between the inner face of a tire body and a rim, by mounting the tire body to the periphery of the rim, is widely used and well known as a tire for automobiles and autocycles, from the viewpoint that a rubber tube is not necessary and handling is easy.
A pneumatic tire supports load and exhibits various properties such as riding comfort by supplying air into the tire and so, maintaining the air pressure within the tire is extremely important.
In order to do so, usually, an inner liner layer comprising rubber with low air permeability, such as butyl rubber and halogenated butyl rubber, is formed on the inner face of the tubeless tire. However, because rubber material has some air permeability, the air within the tire, which was supplied in advance so as to become the specified pressure, gradually leaks over time and the air pressure gradually decreases. As a result, bothersome maintenance, such as periodically inspecting the tire and refilling with air, was necessary.
On the other hand, decrease in fuel consumption is a large technical problem for automobiles and as part of this problem, demands for a lightweight pneumatic tire are becoming stronger. In order fulfill the demands, development of an inner liner, in which air permeability is decreased further, is an urgent task. If such a composition for an inner liner is developed, the inner liner layer can be made thin and lightweight tires can be obtained.
As the inner liner of a pneumatic tire, methods of using various materials instead of rubber with low air permeability, such as butyl rubber, have been suggested. For example, JP-B-47-31761 discloses applying a solution or dispersion solution of synthetic resin, such as polyvinylidene chloride, saturated polyester resin and polyamide resin, with even lower air permeability, to the inner face of the tire. However, the method disclosed in this document has a problem in adhesion between the rubber layer and the synthetic resin layer inside the pneumatic tire and the fault of the inner liner being poor in moisture resistance.
JP-A-5-330397 discloses conducting halogenation treatment of the inner face of the tire and forming thereon a polymer film of methoxy methylated nylon, copolymerized nylon, a mixture of polyurethane and polyvinylidene chloride or a mixture of polyurethane and polyvinylidene fluoride.
JP-A-5-318618 discloses a pneumatic tire having a thin film of methoxy methylated nylon as the inner liner layer. More specifically, the method of spreading or applying a solution or emulsion of methoxy methylated nylon to the inner face of a green tire or the inner face of a vulcanized tire is disclosed. However, the methods disclosed in these documents have the fault of difficulty in maintaining evenness of film thickness, in addition to the fault of the thin film being poor in moisture resistance.
JP-A-6-40207 discloses an example in which a thin film having a layer with low air permeability comprising a polyvinylidene chloride film or a ethylene-vinyl alcohol copolymer film and an adhesive layer comprising a polyolefin-type film, an aliphatic polyamide film or a polyurethane film is used as the air permeability prevention layer. However, in this example, the layer with low air permeability lacks flexibility and the thin film cannot follow the deformation of the material when running the tire, causing cracks.
JP-A-2000-177303 suggests a tubeless tire in which an air impermeable layer comprising an ethylene-vinyl alcohol copolymer formed into a film is bonded and unified to the inner face of the tire body either directly or via an adhesive resin. However, even in such an air impermeable layer comprising an ethylene-vinyl alcohol copolymer, gas barrier properties are insufficient and the time for which the specified air pressure is maintained cannot necessarily be fulfilled. Also, the tire is prepared by bonding the film to the inner face of the tire body formed in advance to a specified shape or by bonding the film to the tire material before molding and then molding into a tire shape. In the case of the former method, because the inner face of the tire body is narrow and concave, evenly bonding the film to the inner face is difficult in terms of operation. Also, unevenness in bonding tends to occur and from such areas, air tends to leak. In the case of the latter method, because the surface of the tire material and surface of the film are bonded, smoothness between the bonded surfaces is required and when smoothness is insufficient, problems such as exfoliation tend to occur.
JP-A-5-508435 suggests using a composition containing carbon black, a plasticizer and a vulcanizer in rubber obtained by halogenating a copolymer of isomonoolefin having 4 to 7 carbon atoms and paraalkylstyrene, as the inner liner. However, decrease in air permeability is insufficient with this inner liner, therefore unsuitable for obtaining lightweight tires.
Also, JP-A-8-259741, JP-A-11-199713, JP-A-2000-63572, JP-A-2000-159936 and JP-A-2000-160024 suggest using a rubber composition obtained by mixing or dynamically crosslinking an elastomer and polyamide resin, polyester resin, polynitrile resin, cellulose resin or fluororesin and imide resin as the inner liner. However, in such rubber compositions, following deformation of other rubber material was extremely difficult, when processing by molding a tire or vulcanizing, and cracks developed when running.